Towards understanding RAFT aqueous heterophase polymerization [Elektronische Ressource] / von Samira Nozari

Informations

• Publié par: universitat_potsdam
• Publié le: 01 janvier 2005
• Nombre de lectures: 38
• Langue: Deutsch
• Poids de l'ouvrage: 5 Mo

Extrait

Max-Planck-Institut für Kolloid- und Grenzflächenforschung



Towards Understanding RAFT Aqueous
Heterophase Polymerization






Dissertation


zur Erlangung des akademischen Grades
"doctor rerum naturalium"
(Dr. rer. nat.)
in der Wissenschaftsdisziplin Kolloidchemie





eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakultät
der Universität Potsdam




von
Samira Nozari





Potsdam, im Mai 2005 Chapter 1: Introduction 1

Table of contents
1. Introduction.....................................................................................................3
2. Theory and Background.................................................................................7
2.1. Free radical polymerization ........................................................................7
2.2. Controlled radical polymerization (CRP) ..................................................10
2.2.1. Stable free radical polymerization (SFRP) .........................................12
2.2.2. Atom transfer radical polymerization (ATRP).....................................13
2.2.3. Degenerative transfer (DT) ................................................................14
2.2.4. Reversible addition-fragmentation transfer (RAFT)............................15
2.3. RAFT: the mechanism..............................................................................16
2.4 Aqueous heterophase polymerization .......................................................24
2.4.1. General description............................................................................24
2.4.2. Compartmentalization........................................................................26
2.4.3. Swelling .............................................................................................27
2.4.4. Solubility ............................................................................................28
2.5. RAFT in aqueous heterophase polymerization ........................................29
3. Methods of Characterization31
3.1. Reaction calorimetry.................................................................................31
3.2. Gel permeation chromatography (GPC)...................................................35
3.3. Dynamic light scattering ...........................................................................38
3.4. Ultraviolet/Visible (UV-Vis) spectroscopy .................................................41
4. Results and Discussion ...............................................................................44
4.1. The Initiators, the RAFT agents, and homogeneous polymerizations ......46
4.1.1. The initiators ......................................................................................46
4.1.2. The RAFT agents...............................................................................48
4.2. RAFT ab-initio emulsion polymerization of styrene ..................................51
4.2.1. Rate of polymerization .......................................................................52
4.2.2. AIBN: polymerization rate, colloidal and molecular properties ...........58
4.2.3. The molecular properties obtained with the other initiators................62
4.2.4. Coagulum formation and colloidal stability.........................................66
4.2.5. Particle size in RAFT ab-initio emulsion polymerization.....................69 Chapter 1: Introduction 2

4.2.6. Number of polymer chains .................................................................71
4.3. Phase transfer of RAFT agents in heterophase polymerization ...............73
4.3.1. The experimental setup and procedure .............................................74
4.3.2. Polymerization of swollen seed particles ...........................................78
4.3.3. Radical entry into latex particles ........................................................81
4.3.4. Transport of different RAFT agents....................................................82
4.3.5. Carrier for the transport......................................................................83
4.3.6. An approach for preparation of composite particles...........................85
4.4. Heterophase polymerization of styrene with RAFT at room temperature.87
4.4.1. The influence of the initiator concentration ........................................87
4.4.2. Time-dependent characteristics at room temperature........................88
4.4.3. The influence of temperature .............................................................90
5. Conclusion and Outlook ..............................................................................93
Appendix ..............................................................................................................I
Appendix I: Categorized Library of Results ........................................................I II: Experimental Section .................................................................. IX
Appendix III: ReferencesXVII IV: Symbols and Abbreviations....................................................XXIV
Acknowledgements ......................................................................................XXIX
Chapter 1: Introduction 3

“It may be that the old astrologers had the truth exactly
reversed, when they believed that the stars controlled the
destinies of men. The time may come when men control the stars.”
Arthur C. Clarke
First on the Moon, 1970

1. Introduction

Human beings either due to their nature or their need to survive have always
struggled to take control of events taking place in their surroundings. This
endeavor has played an important role in all aspects of human way of life, such
as the formation of borders, the structure of societies, and the improvement of
the standard of living. Even today, from making every effort to be able to control
the amount of milk that a farm cow produces to seeking control over the
resources of another country, controlling is everywhere and is done by almost
everyone. We, human beings, want everything to function the way that we desire;
the plants and animals reproduce the way that we wish; the machines and
devices operate the way that we want them; and the materials exhibit the
properties that we fancy. Nowadays, the level of seeking control in science is
both vast and small. Vast in the sense that it covers all aspects of life and small
in the scale of control sought. The new plants and animals have modified genes,
the new devices are molecular motors, and the new materials are, for instance,
nanotubes, and nanoparticles. These days, scientists are engaged in controlled
crystallization, assembly, polymerization, and try to put together atoms,
molecules, and particles in a controlled manner to build up complicated
structures that exhibit unique and novel properties.

The increasing control that chemists are able to exert over molecular architecture
allows for the design and preparation of macromolecular and polymeric systems
1of unprecedented sophistication. Macromolecules -large molecules consisting of Chapter 1: Introduction 4

several repeating units- have a great potential to exhibit new properties when
different combinations, numbers and orders of units are employed in their
structure. However, the polymerization methods that allow for such a level of
structural control are limited not only in numbers but also in the required reaction
conditions. For example, anionic polymerization, the method that provides the
highest level of control, usually requires reaction temperatures below -50°C and
the absolute elimination of oxygen and water. On the other hand, the most
common method of polymerization -also for commercial production of polymers-
2has been free radical polymerization (FRP) because of its simplicity and
tolerance towards all kinds of impurities and auxiliary materials, such as
stabilizers, trace amounts of oxygen, and water. Moreover, the range of the
monomers that can be polymerized by radical means, the molar mass of the
generated polymers, and the range of the reaction temperature are considerably
larger than those in other techniques. Therefore, many different processes such
as bulk, solution, and emulsion polymerization can be applied for FRP.

However, the limitation of this method is the lack of control over the reactivity of
the radicals, which causes the lack of control over the molar mass, molar mass
distribution, end-functionalities, and molecular architecture. Taming free radicals
is an issue since the early days of radical polymerization. The recent emergence
of many so called “living” or “controlled” radical polymerization (CRP) processes
has opened a new area in this “old polymerization” method that had witnessed
relatively small progress in the years before. Nowadays, various CRP techniques
provide simple and robust routes toward the synthesis of well-defined, low-
polydispersity polymers, and the fabrication of novel functional materials. Despite
the advanced developments of these methods in homogeneous systems, their
progress in polymerizations under heterophase c